A speaker is a device for converting an electrical audio signal into a corresponding sound. A variety of speakers have been developed and continue to be improved since the nineteenth century.
In general, an electrodynamic, direct-radiating speaker is mainly composed of a magnetic circuit assembly, a voice-coil partially or wholly inside the magnetic circuit assembly, and a sound-radiating diaphragm mechanically attached to the voice-coil; and in most cases, together with other supporting parts like the diaphragm surround, suspension, also referred to as the spider or the suspension, frame, etc. As a magnetic field resulting from the alternating current flowing through the coil interacts with a magnetic field from the magnetic-circuit assembly according to Fleming's rules, the voice-coil actuates the attached portion of the diaphragm, thus the portion of the diaphragm vibrates, and propagates such vibration to the rest of the diaphragm area not directly attached to the voice-coil. As a result, the sound radiates from the whole diaphragm area in a very complex manner due to the frequency-dependent and non-linearity in the sound-propagation, absorption (damping), and boundary reflection process. Therefore, the material, structure and configuration of the diaphragm significantly influences the sound quality of the speaker.